This invention relates generally to gauges and in particular to an ultrasonic depth gauge for liquids under high pressure.
In certain applications it is desirable or necessary to use a pressurized gas to transfer a liquid from one location to another; for example, to transfer cryogenic liquids from a holding vessel to a rocket engine, or to transfer cooling water from a storage vessel to components situated in a high-temperature environment. Conventional instrumentation to measure liquid depth does not have the capability to operate under the extreme pressures which prevail in many such liquid transfer systems.
Prior methods of liquid level sensing operated on one of four principles: (1) floats, (2) conductances (resistances), (3) ultrasonics or (4) hydrostatic pressures. The float type indicator has a float in contact with the liquid. As the liquid level varies, the float moves along a sensing device which indicates the liquid level. The conductance (or resistance) type of sensor has probes, which contact the liquid at a certain height. When the liquid contacts the probes, an electric circuit is completed indicating the liquid level. The ultrasonic sensor works in one of two ways. With the first method, the liquid fills a gap between a ultrasonic transmitter and reflector at a certain level. The ultrasonic transmission propagates to and from the reflector when the gap is filled by the liquid. The second method involves measuring the time required for an ultrasonic pulse to propagate from a transducer through the gas above the liquid, to the surface of the liquid, and back to the transducer. The transmit time is proportional to the height of the liquid. However, none of the above systems are suitable for measuring the depth of a liquid under extremely high gas pressurization (ie: exceeding 3000 p.s.i.).
The fourth method uses hydrostatic pressure to measure the level of a liquid. The pressure at a particular point of a liquid varies with the height of the liquid above that point. Thus, measuring the pressure at the bottom of a liquid indicates the height of the liquid. Generally, however, the hydrostatic pressure type suffers a limitation too. When a liquid is pressurized, the hydrostatic device will yield a false indication of liquid depth.
Thus, it is the object of the present invention to provide a method and apparatus to accurately and continuously measure the depth of a liquid subjected to extremely high gas pressurization.
It is a further object of the present invention to employ a depth gauge apparatus that is impervious to extreme high pressures.
Other objects and advantages of the present invention will be readily apparent from the following description and drawings which illustrate a preferred embodiment of the present invention.